/Engine/Source/Editor/LevelEditor/Public/LevelEditorOutlinerSettings.h
so you cannot rely on the filter to know which outliner it is active in.Usethe override that takes a delegate instead
void AddCustomFilter ( [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [FFilterBase](API\Developer\ToolWidgets\Filters\FFilterBase)< const [ISceneOutlinerTreeItem](API\Editor\SceneOutliner\ISceneOutlinerTreeItem) & >> InCustomFilter )